Point emission type light emitting element and concentrating point emission type light emitting element

ABSTRACT

To provide a point emission type light emitting element that restricts the light emitting area within a sufficiently tiny region and can be manufactured at a low cost, the point emission type light emitting element is a light emitting element that has stripe ridge comprising an n-type layer, an active layer and a p-type layer that are formed from semiconductors on a substrate, so as to emit light from one end face of the stripe ridge, wherein the stripe ridge has a protruding portion on the end face described above and the surface of the light emitting element is covered with an shading film except for the tip of the protruding portion.

BACKGROUND OF THE INVENTION

[0001] b 1. Field of the Invention

[0002] The present invention relates to a point emission type lightemitting element having a light emitting area restricted within a tinyregion, and to a concentrating point emission type light emittingelement that concentrates light emitted thereby and outputs the lightthrough a tiny region.

[0003] 2. Description of the Related Art

[0004] The present applicant already developed nitride semiconductorlight emitting diodes that emit blue and green light with high outputpower and are used in practical applications as light sources for largeimage display apparatuses. The nitride semiconductor light emittingelement is manufactured, for example, by forming p-type and n-type ohmicelectrodes on a multi-layer semiconductor film that is formed from anitride semiconductor of GaN, AlN, InN or a mixed crystal thereof on asapphire substrate, and separating the elements into chips by suchprocesses as cleaving, RIE etching or dicing. The light emitting elementmade as described above emits light not only from a light emitting layerbut also from cut-off surfaces and principal plane of the substrateafter causing the light to repeat transmission through the othersemiconductor layers and in the substrate, refraction and reflectiontherein.

[0005] In recent years, there have been increasing demands for lightemitting elements that restrict the light emitting area within amicroscopic region for such applications as the light sources foroptical communication, electrophotography and virtual reality display.To meet these demands, nitride semiconductor light emitting elements ofvarious constitutions have been proposed with the light emitting arearestricted within a microscopic region.

[0006] An end face emitting type light emitting element has beenproposed as a light emitting element having microscopic light source.The end face emission light emitting element employs doubleheterojunction structure wherein a light emitting layer is sandwiched byforming p-type and n-type semiconductor layers that have wide band gap,as the basic structure similarly to a semiconductor laser. For example,an end face emission type light emitting diode made of nitridesemiconductor employs separation-confinement heterojunction structure(SCH) based on AlGaN/GaN/InGaN.

[0007] However, in the constitution of the proposed light emittingelement that restricts the light emitting area within a microscopicregion, a high accuracy of patterning is required to restrict the lightemitting area within the microscopic region, and an advancedphotolithography technology must be used. This results in the problemthat the light emitting element that restricts the light emitting areawithin the microscopic region cannot be provided at an economical price.

[0008] Although the end face emission type light emitting diode can bemade with small spot size, multi-mode light emission is produced sincelight is emitted not only from the end face of the light emitting layerbut also from the end faces of the n-type semiconductor layer formednearer to the substrate than the light emitting layer, thus making itunsuitable for such applications as a single spot of good near-fieldpattern is required.

SUMMARY OF THE INVENTION

[0009] Thus, a first object of the present invention is to provide apoint emission type light emitting element that restricts the lightemitting area within a sufficiently tiny region and can be manufacturedat a low cost, and a method of manufacturing the same.

[0010] A second object of the present invention is to provide aconcentrating point emission type light emitting clement that produces asingle spot light of good near-field pattern with a high efficiency oflight emission.

[0011] The point emission type light emitting element according to thepresent invention to meet the first object described above is a lightemitting element that has stripe ridge comprising an n-type layer, anactive layer and a p-type layer that are formed from semiconductors on asubstrate, so as to emit light from one end face of the stripe ridge,wherein the stripe ridge has a protruding portion on the end facedescribed above and the surface of the light emitting element is coveredwith an shading film except for the tip of the protruding portion.

[0012] In the point emission type light emitting element of the presentinvention constituted as described above, since the surface of the lightemitting element is covered with the shading film except for the tip ofthe protruding portion, light emitting area can be restricted to the tipof the protruding portion.

[0013] Therefore, according to the present invention, light can beemitted only from the tip of the protruding portion, and the lightemitting area can be made extremely small by setting the width of theprotruding portion in accordance to the light emitting area that isrequired.

[0014] Also because the surface of the light emitting element is coveredwith the shading film except for the tip of the protruding portion,leakage of light from other portions than the tip of the protrudingportion can be suppressed, thereby increasing the efficiency of lightemission.

[0015] Also the n-type layer, the active layer and the p-type layer ofthe point emission type light emitting element of the present inventioncan be formed from nitride semiconductors, which makes it possible toemit light of relatively short wavelength.

[0016] The method of manufacturing the point emission type lightemitting element according to the present invention is, in order toachieve the first object described above, a method of manufacturing thepoint emission type light emitting element by forming a plurality ofelements on the substrate and dividing the substrate with layers formedthereon into individual elements, and comprises a step of forming then-type layer, the active layer and the p-type layer on the substrate oneon another, a step of forming stripe ridge that has a neck portionformed near one end thereof having narrower width than the other portionin correspondence to the elements described above, a step of formingshading films at least on one end face of the stripe ridge and the topsurface and both side faces of the neck portion, and a step of dividingthe elements at the neck portion along a direction perpendicular to thelongitudinal direction of the stripe ridge.

[0017] According to the method of manufacturing the point emission typelight emitting element of the present invention constituted as describedabove, the light emitting element having the light emitting arearestricted within a tiny region located at the end of the stripe ridgecan be easily manufactured, and the light emitting area that hasextremely small light emitting area can be manufactured at a low cost.

[0018] The concentrating point emission light emitting element accordingto the present invention to meet the second object described above is asurface emission type light emitting element made in stackedsemiconductor structure of double heterojunction structure wherein anactive layer is sandwiched by a p-type semiconductor layer and an n-typesemiconductor layer that have band gap larger than that of the activelayer so as to emit light from a light emitting point Located in thesurface of the p-type semiconductor layer, where such a pyramidalsurface is provided in the stacked semiconductor structure located rightbelow the light emitting point that reflects the light upward orretracts the light, the stacked semiconductor structure is divided intoa plurality of light emitting regions located around the pyramidalsurface that is at the center, and ridges of smaller width than thelight emitting region are s formed on the p-type semiconductor layer sothat light emitted from the light emitting regions is directed towardthe pyramidal surface.

[0019] In the concentrating point emission type light emitting elementof the present invention constituted as described above, since thewaveguide is formed in each of the light emitting regions, that lightemitted in the light emitting regions is directed toward the lightemitting point so as to be reflected or refracted by the pyramidalsurface and is output through a narrow region, and therefore the elementcan be used as a point light source.

[0020] The concentrating point emission type light emitting element ofthe present invention is also capable of emitting light with a highluminance since light emitted in all light emitting regions isconcentrated and output together.

[0021] Moreover, since the concentrating point emission type lightemitting element of the present invention can concentrate light into asmall region and output the light therefrom, a light spot of single modehaving good near field pattern can be produced.

[0022] In the concentrating point emission type light emitting elementof the present invention, the plurality of light emitting regions can beformed by separating the light emitting regions from each other byetching the borders between adjacent light emitting regions to a depthmidway in the n-type semiconductor layer in the stacked semiconductorstructure except for the light emitting point and a vicinity thereof,and forming n-type electrode on the n-type semiconductor layer that hasbeen exposed by etching.

[0023] In the concentrating point emission type light emitting elementof the present invention, the pyramidal surface can be constituted froma pyramidal cavity that has an apex located in the light emergingdirection and is formed in the stacked semiconductor structure.

[0024] Moreover, in the concentrating point emission type light emittingelement of the present invention, the pyramidal surface can also beformed by filling a recess of pyramidal shape, that expands toward thelight emerging point and is formed so as to reach at least the n-typesemiconductor layer in the stacked semiconductor structure, with atransparent material having a refractive Index higher than that of theactive layer.

[0025] In the concentrating point emission type light emitting elementof the present invention, the pyramidal surface is preferably a conicalsurface, which makes it possible to produce spot light of near truecircle.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is a perspective view showing the constitution of a nitridesemiconductor light emitting element according to first embodiment ofthe present invention.

[0027]FIG. 2 is a perspective view after nitride semi conductor layerthat constitutes the element is formed on a sapphire substrate in themanufacturing process of the nitride semiconductor light emittingelement according to the first embodiment of the present invention.

[0028]FIG. 3 is a perspective view after a ridge stripe and elementregions are formed by etching in the manufacturing process of thenitride semiconductor light emitting element according to the firstembodiment of the present invention.

[0029]FIG. 4 is a perspective view after a p-type electrode and ann-type electrode are formed in the manufacturing process of the nitridesemiconductor light emitting element according to the first embodimentof the present invention.

[0030]FIG. 5 is a perspective view after a p pad electrode and an n padelectrode are formed in the manufacturing process of the nitridesemiconductor light emitting element according to the first embodimentof the present invention.

[0031]FIG. 6 is a perspective view after an shading film is formed tocover the top surface of the element in the manufacturing process of thenitride semiconductor light emitting element according to the firstembodiment of the present invention.

[0032]FIG. 7 is an enlarged perspective view showing the end of theridge stripe in the nitride semiconductor light emitting elementaccording to the first embodiment of the present invention.

[0033]FIG. 8 is a partial plan view of a concentrating point emissiontype light emitting element according to second embodiment of thepresent invention.

[0034]FIG. 9 is a sectional view taken along lines A-A′ of FIG. 8.

[0035]FIG. 10 is a sectional view taken along lines B-B′ of FIG. 8.

[0036]FIG. 11 is a sectional view of stacked semiconductor structuregrown in the manufacturing process of the concentrating point emissiontype light emitting element according to the second embodiment of thepresent invention.

[0037]FIG. 12 is a plan view of the stacked semiconductor structureafter forming a light emitting region therein in the manufacturingprocess of the concentrating point emission type light emitting elementaccording to the second embodiment of the present invention.

[0038]FIG. 13 is a plan view after forming a ridge in each lightemitting region in the manufacturing process of the concentrating pointemission type light emitting element according to the second embodimentof the present invention.

[0039]FIG. 14 is a plan view after forming a p-type electrode in eachlight emitting region and an n-type electrode between adjacent lightemitting regions in the manufacturing process for the concentratingpoint emission type light emitting element according to the secondembodiment of the present invention.

[0040]FIG. 15 is a plan view after forming an insulation film 113 thatfills the light emitting region in the manufacturing process for theconcentrating point emission type light emitting element according tothe second embodiment of the present invention.

[0041]FIG. 16 is a plan view after forming p pad electrodes that connectthe p-type electrodes of all light emitting regions in the manufacturingprocess for the concentrating point emission type light emitting elementaccording to the second embodiment of the present invention.

[0042]FIG. 17 is a plan view showing the electrodes arrangement in theconcentrating point emission type light emitting element according tothe second embodiment of the present invention.

[0043]FIG. 18 is a sectional view showing the constitution of arefracting pyramidal surface of a variation according to the presentinvention.

[0044]FIG. 19 is a plan view showing the light emitting region of avariation according to the present invention.

[0045]FIG. 20 is a sectional view showing the constitution of a cavity152 b (opening at the top) of a variation according to the presentinvention.

[0046]FIG. 21 is schematic sectional view showing the state of emittinglight in the case of using a cavity closed at the top (a) and in thecase of using a cavity open at the top (b)

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] Now the point emission type light emitting element according topreferred embodiments of the present invention will be described belowwith reference to the accompanying drawings.

EMBODIMENT 1

[0048] The point emission type light emitting element according to thefirst embodiment of the present invention is a nitride semiconductorlight emitting diode. The point emission type light emitting element hassuch a constitutions as an n-type layer 12, an active layer 13 and ap-type layer 14 that are formed from nitride semiconductors on asubstrate 10 made of sapphire via a buffer layer 11, with a stripe ridge20 that has a protruding portion 21 a being formed on one end facethereof, while being covered with an shading film 31 substantiallyentirely except for the tip of the protruding portion 21 a, as shown inFIG. 1. The point emission type light emitting element is manufacturedas described below.

[0049] First, as shown in FIG. 2, the buffer layer 11 made of GaN grownat a low temperature, for example, the n-type layer 12 made of GaN dopedwith Si, for example, the active layer 13 made of InGaN, for example,and the p-type layer 14 made of GaN doped with Mg, for example, areformed successively on the substrate 10.

[0050] Then stripe ridges 20 are formed in regions that correspond tothe elements, and 2-step etching operation is carried out as describedbelow in order to define the element regions.

[0051] In the first etching process, a first mask is formed in a regionwhere the stripe ridge 2—would be formed, and the portion not covered bythe first mask is etched by reactive ion etching (RIE) midway in depthof the n-type layer 12. The first mask used in the first etching processis formed in such a configuration as portions that correspond to frontand back sides of a cleavage surface located on one end of the striperidge 20 are made narrower than the other portions, so that a narrowneck portion 21 is continuously formed on the end face of the striperidge 20 after etching.

[0052] Longer axis of the stripe ridge 20 and longer axis of the neckportion 21 preferably agree with each other.

[0053] Width of the stripe ridge is not limited to a particular value,but is preferably in a range from 1 to 100 μm, and more preferably in arange from 5 to 50 μm. When the width is less than 1 μm, it is difficultto precisely form the stripe ridge 20 and the narrower neck portion 21by etching. When the width is greater than 100 μm, loss of light due tothe nitride semiconductor increases when the light generated in theactive layer is directed through the ridge 20 that is wider. When thewidth is 5 μm or greater, the stripe ridge 20 and the narrower neckportion 21 can be formed precisely by etching, and width within 50 μmmakes it possible to minimize the loss of light and cause the light toemerge through one end face. The width is set to 20 μm in thisembodiment.

[0054] According to the present invention, there is no limitation to thewidth of the neck portion 21 that can be determined by setting thestripe width and particularly the width of the end face that is obtainedat the last, so that a light source of desired small size can be formed.Stripe width at the neck portion 21 is preferably set in a range from 1to 10 μm. When the width is less than 1 μm, it is difficult to preciselyform the neck portion 21 by etching. Width greater than 10 μm is notsuitable for the tiny light source. Width of the neck portion 21 is setin a range from 2 to 3 μm in this embodiment. According to the presentinvention, there is also no limitation to the length of the neck portion21 that can be set so that it is convenient for cleaving operation toobtain the end face. Specifically, the length is preferably set in arange from 1 to 50 μm, and more preferably in a range from 5 to 30 μm.When the length is less than 1 μm, there arises a problem related to theaccuracy in etching. Length of 5 μm or larger makes it possible tocleave at the neck portion 21 where there is less probability of defectsbeing included. When cleaving a material such as sapphire that isdifferent from the nitride semiconductor, there is a possibility ofcleaving to take place at a wrong place, and a length less than 5 μmincreases the possibility of much cleavage defects to occur in the neckportion 21, that can be reduced by setting the length to 5 μm or larger.Although cleavage can be carried out without increasing the number ofcleavage defects when the length is larger than 50 μm, this reduces thenumber of chips produced per wafer. When the length is 30 μm or less,good cleavage and satisfactory yield of production can be achieved,while securing a certain number of chips produced per wafer. The lengthis set to 10 μm in this embodiment.

[0055] In the second etching process, a second mask is formed over thearea except for the separation regions where the elements are to bedivided, leaving the first mask used in the first etching process toremain, and the nitride semiconductor layer is removed from theseparation regions by etching midway in depth of the buffer layer 11 orto the surface of the substrate 10.

[0056] Thus the 2-step etching process results in the element regionseach having the stripe ridge 20 and the neck portion 21 being formed incorrespondence to the elements to be separated (FIG. 3).

[0057] Then as shown in FIG. 4, a p-type ohmic electrode 41 is formed onthe p-type layer 14 of the stripe ridge 20, and an n-type ohmicelectrode 43 is formed on the surface of the n-type layer that isexposed on the outside of one side face of the stripe ridge 20.

[0058] The entire surface of the wafer is covered with a SiO₂ film (notshown) except for the top surface of the p-typo ohmic electrode 41 andthe top surface of the n-type ohmic electrode 43 of each electroderegion. Then a p pad electrode 42 is formed in contact with the p-typeohmic electrode 41 that is exposed through the opening in the Si₂ film,and an n pad electrode 44 is formed in contact with the n-type ohmicelectrode 43 that is exposed through the opening in the SiO₂ film (FIG.5).

[0059] As shown in FIG. 5, the n pad electrode 44 is formed so as tooverlap with the n-type ohmic electrode 43, and the p pad electrode 42is formed so as to make contact with p-type ohmic electrode on the topsurface of the stripe ridge 20 and extend therefrom over the other sideface of the stripe ridge 20 and over the SiO₂ film located on theoutside of the side face.

[0060] Then a mask is formed to cover the n pad electrode 44 and thevicinity thereof and the p pad electrode 42 and the vicinity thereof.The mask is used to form a metal film (shading film) of Cr/Au (Au filmformed over a thin film of Cr) covering the entire wafer with a vapordeposition or sputtering apparatus. Thus the shading film 31 is formedto cover substantially the entire surface of the wafer including oneside face of the stripe ridge 20 and both side faces of the neck portion21.

[0061] At this time, the top surface of the wafer is covered by eitherthe n pad electrode 44, the p pad electrode 42 or the shading film 31except for the small areas of the n pad electrode 44 and the vicinitythereof and the p pad electrode 42 and the vicinity thereof.

[0062] The shading film 31, the n pad electrode 44 and the p padelectrode 42 are electrically isolated around the n pad electrode 44 andaround the p pad electrode 42.

[0063] Then the wafer is divided into individual elements and theshading film 31 is formed on the side faces of the substrate 10 afterseparation.

[0064] The wafer having the shading film 31 formed on the top surfacethereof is stuck on a heat sensitive sheet with the electrode surface(top surface) facing the sheet, and the wafer is scribed on the backsurface.

[0065] The scribe line perpendicular to the longer side of the ridgestripe 20 is formed at such a position as cross the neck portion 21 atright angles at the center of the neck portion 21.

[0066] After sticking the scribed back surface of the wafer onto a diebonding sheet, the heat sensitive sheet is peeled off the wafer surface.

[0067] The individual element chips are separated from each other with aspace produced in between by pulling the die bonding sheet to expandevenly in all directions.

[0068] The end face at the tip of the protruding portion 21 a of eachchip that has been separated is a cleavage surface created after formingthe shading film 31 on the top surface of she wafer, and therefore isnot covered by the shading film.

[0069] Then the electrode surfaces of the chips are pressed against anadhesive layer of an adhesive sheet, with the adhesive layer being 10 μmthick, to be stuck thereon while maintaining the distance between thechips, and the die bonding sheet is removed. At this time the chips arearranged on the adhesive sheet in an array with a predetermined distancefrom each other and the hack surface of the sapphire substrate 11 facingup. Each chip is secured onto the adhesive sheet with the electrodesurface being pressed against the adhesive layer with a relatively largeforce, while providing masking function to prevent the shading film frombeing formed on the top surface of the chip, particularly on the endface of the protruding portion 21 a of each chips during the process offorming the shading film on the back surface and the side faces of thesubstrate.

[0070] Then the chips arranged on the adhesive sheet in an array with apredetermined distance from each other with the back surface of thesubstrate facing up are set in a vapor deposition or sputteringapparatus, where a Cr film (600 Å thick, for example) and an Au film(2400 Å thick, for example) are formed successively, thus forming theshading film 31 on the back surface and the side faces of the substrate.

[0071] In the process described above, the nitride semiconductor lightemitting elements are manufactured in the form of separated chips thatare substantially totally covered, except for the end face of theprotruding portion 21 a formed to protrude from one end face of thestripe ridge 20, by either the n pad electrode 44, the p pad electrode42 or the shading film 31 that shield light.

[0072] This provides the point emission type light emitting element thatis capable of emitting light on one end face of the stripe ridge, orfurther from limited region of the end face of the protruding portion 21a.

[0073] The point emission type light emitting element of the firstembodiment that emits light from the end face of the protruding portion21 a allows it to easily restrict the light emitting area within anextremely small region by forming the protruding portion 21 a with asmall width.

[0074] That is, while it is difficult to restrict the light emittingarea by forming the shading film in a predetermined pattern on the endface of the stripe ridge, the constitution and the manufacturing methodof the first embodiment makes it possible by a unique technique asfollows: the narrow neck portion 21 is continuously formed on the endface of the stripe ridge and cleavage is carried out at the neck portion21 after forming the shading film, and the light emitting area isrestricted further within a narrow region on the light emitting end faceof the stripe ridge, so that the light emitting area can be easilyrestricted within an extremely small region.

[0075] While the first embodiment has been described above, the presentinvention is not limited to the first embodiment and variousmodifications can be made and various materials can be used as describedbelow.

VARIATION OF EMBODIMENT 1

[0076] For the substrate used in the present invention, insulatingsubstrate such as sapphire or spinel (MgAl₂O₄) that has principal planein C plane, R plane or A plane, SiC (including 6H, 4H, 3C), ZnS, ZnO,GaAs, Si and oxide substrate that makes lattice matching with nitridesemiconductor have been known as materials different from nitridesemiconductor. Sapphire and spinel are preferably used. A nitridesemiconductor substrate such as GaN and AlN can also be used.

[0077] As the nitride semiconductor formed on the substrate, III-V groupgallium nitride compound semiconductor materials can be used. Forexample, In_(x)Al_(y)Ga_(1-x-y)N (0≦x≦1, 0≦y≦1, 0≦x+y≦1), and InAlGaBN,InAlGaNP and InAlGaNAs made by adding B to the III group element orsubstituting a part of V group element N with As or P can be used. Goodlight emitting layer can be obtained by using In_(u)Al_(v)Ga_(1-u-v)N(0<u 1≦v<1, 0≦u+v<1). As the n-type impurity used for the nitridesemiconductor of the present invention, IV group element such as Si, Ge,Sn, S, O, Ti or Zr, or VI group element nay be used. Good carrier can begenerated by preferably using Si, Ge and Sn, and most preferably usingSi. While there is no limitation to the p-type impurity, Be, Zn, Mn, Cr,Mg or Ca may be used, and Mg is preferably used. Thus the n-type nitridesemiconductor and the p-type nitride semiconductor that constitute then-type layer and the p-type layer can be formed.

[0078] The relationship between the stripe ridge 20 and the neck portion21 in the present invention is not limited to the configuration shown inFIG. 3, making the neck portion 21 narrower than the ridge stripe 20 soas to form the tiny light source of the desired shape and size on theneck portion.

[0079] That is, while the stripe ridge 20 and the neck portion 21 may beformed as a stripe of substantially uniform width as shown in FIG. 3,the stripe may also be formed in a tapered configuration with the widththereof varying with the position along the longitudinal direction.Specifically, the stripe may be formed in such a tapered configurationas the width of the stripe ridge 20 decreases toward the neck portion 21and the end face along the longitudinal direction, thereby increasingthe efficiency of extracting light by concentrating the light emitted bythe stripe ridge 20 into the neck portion 21. The stripe ridge 20 may betapered over the entire length thereof or in a section thereof, forexample from the joint with the neck portion 21 over some length alongthe stripe 20, as in the example described above. Similar configurationmay be employed also for the neck portion 21.

[0080] Although the ridge stripe of the present invention is formedmidway in depth of the n-type layer 12 as shown in FIG. 3, the presentinvention is not limited to this configuration, and the ridge stripe 20may be formed by etching to such a depth that does not reach the activelayer 13. When the ridge stripe 20 is formed above the active layer 13,such a structure can be formed as degradation of the active layer 13 dueto exposure to atmosphere is retarded. The effect of preventingdegradation of the active layer 13 becomes more conspicuous when thestripe is formed with a small width of 10 μm or less. On the other hand,since a desired tiny light source is made by using one end face of theneck portion 21 as a light emerging surface, it is preferable to etchinto such a depth that reaches the n-type layer, deeper than the activelayer 13. Etching depth in the neck portion 21 and in both sides of thestripe ridge 20 may be changed according to the functions thereof.

[0081] While the stripe ridge 20 and the neck portion 21 join at asurface substantially perpendicular to the longitudinal direction of thestripe ridge 20, the present invention is not limited to thisconfiguration. The stripe ridge 20 and the neck portion 21 may also bejoined at a surface having an angle less than 90° from the longitudinaldirection so that, for example, the joint is also tapered. Thisconfiguration makes it possible to efficiently direct light from thestripe ridge 20 to the neck portion 21, and improve the efficiency ofextracting light by decreasing the loss of light due to reflection atthe joint.

[0082] There is no limitation to the shading film that may be made ofany material as long as the light emitted by the light emitting elementcan be shielded, and TiO and SiO that absorb light and metals such asCr, Ti/Pt, Ti, Ni, Al, Ag and Au may be used. Also at least one kindselected from among a group consisting of SiO₂, TiO₂, ZrO₂, ZnO, Al₂O₃,MgO and polyimide may be used to form a multi-layer dielectric filmcomprising films λ/4 n thick (λ is wavelength and n is the refractiveindex of the material) of such a material.

[0083] Furthermore, the present invention is not limited to nitridesemiconductor.

[0084] According to the present invention, as described above, variousmodifications and various materials can be used to achieve the effectsof the first embodiment.

EMBODIMENT 2

[0085] Now a concentrating point emission type light emitting elementaccording to the second embodiment of the present invention will bedescribed below with reference to the accompanying drawings.

[0086] The concentrating point emission type light emitting element ofthe second embodiment has a plurality of light emitting regions 200formed in radial direction around a light emitting point 150 located atthe center thereof as shown in FIG. 8, so that light emitted by thelight emitting regions 200 is directed through waveguides formed in thelight emitting regions 200 to near the center of the radialconfiguration and emerges from the light emitting point 150.

[0087] In the concentrating point emission type light emitting elementof the second embodiment, the light emitting regions 200 are formed byetching a stacked semiconductor structure, consisting of a buffer layer102, an n-type contact layer 103, an n-type cladding layer 104, anactive layer 105, a p-type cladding layer 106 and a p-type contact layer107 formed one on another successively on a substrate 101, until then-type contact layer 103 is exposed in a radial pattern with the lightemitting point 150 located at the center thereof (FIG. 8 through FIG.10).

[0088] Thus a plurality of the light emitting regions 200 having thestacked semiconductor structure are formed, consisting of the bufferlayer 102, the n-type contact layer 103, the n-type cladding layer 104,the active layer 105, the p-type cladding layer 106 and the p-typecontact layer 107 formed one on another successively on the substrate101, where the waveguides are directed toward the light emitting point150 radially, with the n-type contact layer 103 being exposed betweenadjacent light emitting regions 200 (FIG. 8, FIG. 10).

[0089] According to the second embodiment, the active layer 105 is madeof InGaN, for example, while the n-type cladding layer 104 and thep-type cladding layer 106 are made of AlGaN, for example, that haslarger band gap than the active layer 105, and the light emittingregions 200 have double heterojunction structure. In the secondembodiment, the active layer 105 can be formed in various structuressuch as multiple quantum well structure and single quantum wellstructure, and the mixing ratio of Al in the n-type cladding layer 104and in the p-type cladding layer 106 may be set to an appropriate valueby taking account of such factors as the confinement of light in thelongitudinal direction Further according to the second embodiment, inorder to improve the crystallinity, a base layer may be formed bylateral growth so as to form the n-type cladding layer 104, the activelayer 105 and the p-type cladding layer 106 thereon.

[0090] In the light emitting regions 200 of the concentrating pointemission type light emitting element of the second embodiment, a ridge130 is formed by etching the p-type semiconductor layers (the p-typecladding layer 106 and the p-type contact layer 107) on both sidesthereof midway in depth of the p-type cladding layer 106 so that themiddle portion of a predetermined width remains, and a p-type electrode111 is formed to make ohmic contact only with the top surface of theridge 130 (surface of the p-type contact layer 107 in the ridge 130) viaan opening of the insulation film 108 (FIG. 8, FIG. 10).

[0091] With this constitution, the active layer located right below theridge 130 has an effective refractive index higher than that of theactive layer on both sides thereof so that light is confined right belowthe ridge 130 and is directed along the ridge 130.

[0092] Width of the ridge is preferably set in a range from 1 to 5 m,more preferably in a range from 1.5 to 3 μm, in order to effectivelydirect the light.

[0093] Confinement of light in the direction of depth is achieved bysandwiching the active layer 105 with the n-type cladding layer 104 andthe p-type cladding layer 106 that have lower refractive index.

[0094] According to the second embodiment, it is preferable to form amirror film for reflecting the light on the end face (used formonitoring and therefore hereinafter referred to as monitoring end face)located opposite to the light emitting point 150 of the light emittingregion 200. The mirror film formed on the monitoring end face makes itpossible to reduce the loss caused by unnecessary radiation and improvethe efficiency of light emission, since light reflected on the end facecan be output through the light emitting point 150. In the case of thisconstitution, light reflected on the monitoring end face can beamplified and output through the light emitting point depending on theconditions, so that more effective light emission can be achieved. Themirror film may be a multi-layer electric film made of SiO₂ and TiO₂,with the film thickness preferably set to nλ/4 (n=1, 2, 3 . . . , λ iswavelength of light in the dielectric material), and preferably consistof two or more pair of the layers in order to achieve satisfactoryreflection characteristic. Further in the second embodiment, it ispreferable to form the mirror film from the same material as theinsulation film 113 at the same time therewith in the same process, soas to simplify the manufacturing process and reduce the manufacturingcost.

[0095] According to the second embodiment, the n-type electrode 112 isformed on the n-type contact layer 103 that is exposed between adjacentlight emitting regions 200 (FIG. 8, FIG. 10).

[0096] Also according to the second embodiment, a cavity 152 of conicalshape that has an apex located in the direction of emerging light isformed in the stacked semiconductor structure right below the lightemitting point 150 as shown in FIG. 9, so that light emitted in thelight emitting regions 200 is reflected on the conical surface 153 ofthe cavity 152 upward and is output through an opening (the lightemitting point 150) of the p-type electrode 111.

[0097] Now the method of manufacturing the concentrating point emissiontype light emitting element of the second embodiment will be describedbelow by making reference to examples of materials to be used.

Process to Form a Mask 151

[0098] According to this manufacturing method, a mask 151 is formed forthe purpose of forming the cavity 152 on the substrate 101 as shown inFIG. 11.

[0099] According to the second embodiment, while insulating substratesuch as sapphire or spinel (MgAl₂O₄) that has principal plane in Cplane, R plane or A plane, or semiconductor substrate such as SiC(including 6H, 4H, 3C), Si, Zn, GaAs, GaN may be used, sapphiresubstrate or GaN substrate that can be grown with good crystallinity ispreferably used when nitride semiconductor is employed.

[0100] The substrate 101 is preferably made of a material that has arefractive index higher than that of the semiconductor layer to beformed thereon by 0.2 or more.

[0101] The mask 151 is exposed to a high temperature of 1000° C. orhigher when growing semiconductor layers in the following process, andtherefore must be made of a material that does not decompose at suchtemperatures and does not allows the semiconductor to grow thereon. Assuch, SiO₂, SiN, W or the like can be used.

[0102] The mask 151 is preferably formed in a round (cylindrical) shape,which makes it possible to form the cavity 152 of conical shape in thestacked semiconductor structure that produces spot light of near truecircle.

[0103] While diameter of the mask 151 is determined according to therequired spot diameter, the mask diameter is preferably set in a rangefrom 0.5 to 20 μm, more preferably in a range from 1 to 10 μm in orderto obtain satisfactory light of single mode.

Process to Grow the Semiconductor Layers

[0104] Then the buffer layer 102 having thickness of 200 Å made of GaN,for example, an n-type contact layer 103 a made of GaN having thicknessof 4 μm doped with 4.5×10¹⁸/cm³ of Si, for example, an n-type claddinglayer 104 a made of Al_(0.1)Ga_(0.9)N having thickness of 1 μm dopedwith 1×10¹⁸/cm³ of Si, for example, an active layer 105 a made ofTn_(0.37)Ga_(0.63)N having thickness of 0.09 μm, for example, a p-typecladding layer 106 a made of Al_(0.1)Ga_(0.9)N having thickness of 0.5μm doped with 2>10¹⁸/cm³ of Mg, for example, and a p-type contact layer107 a made of p-type GaN having thickness of 150 Å doped with 1×10¹⁸/cm³of Mg, for example, are formed successively on the substrate 101 havinga mask formed thereon (FIG. 11).

[0105] Through the process described above, the stacked semiconductorstructure having the cavity 152 of conical shape is formed on the mask151 as shown in FIG. 11.

Etching for Forming the Light Emitting Regions

[0106] Then an SiO₂ film having thickness of 0.5 μm is formed on thestacked semiconductor structure by the plasma CVD process. This isfollowed by the formation of a plurality of fan shaped patterns inradial arrangement with the apex located at the center of the mask 51 byphotolithography technique, with the SiO₂ film being etched by, forexample, RIE process The plurality (48 in this embodiment) of fan shapedlight emitting regions 200 are formed by etching the portions notcovered by the SiO₂ film by, for example, the RIE process until then-type contact layer 103 is exposed (FIG. 5). All the light emittingregions 200 are formed to have the same radial dimension and apex angleof the fan shape, and are connected to each other at the apex. The maskmay be made of a material other than SiO₂ film, such as dielectricmaterial including SiN or photo-resist material. Further, the mask maybe formed by a process other than the plasma CVD, such as magnetronsputter or ECR process.

Formation of the Ridge

[0107] After forming an etching mask (made of SiO₂, for example) ofuniform width (for example, 2 μm wide and 0.5 μm thick) for forming theridges on the top surfaces of the light emitting regions 200, both sidesof the etching mask are etched away midway in depth of the p-typecladding layer 106, thereby to form the ridges 130 in the light emittingregions 200 (FIG. 13).

Formation of the P-Type Electrode

[0108] Then an insulation layer 8 (for example, ZrO₂ film havingthickness of 0.2 μm or less) is formed to cover the portions other thanthe top surfaces of the ridges in the light emitting regions 200, andthe p-type electrodes 111 ate formed so as to make ohmic contact withonly the top surfaces of the ridges that are exposed as shown in FIG.14.

[0109] The p-type electrodes Ill are formed from Ni (100 Å)/Au (1500 Å),for example, that can make good ohmic contact with the p-type GaN layer.

Formation of the N-Type Electrode

[0110] Then the n-type electrode 112 is formed on the n-type contactlayer 103 that has been exposed between the adjacent light emittingregions (FIG. 14).

[0111] The n-type electrode 112 is formed from Ti (100 Å)/Al (5000 Å),for example, that can make good ohmic contact with the n-type GaN layer.

[0112] The n-type electrode 112 is formed over the entire surface of then-type contact layer 103 (over-all electrode section) on the outside,with a predetermined distance in between, of the outer periphery(external arc) of the light emitting regions (outside of a circle havinga radius a little larger than the radial dimension of the fan shapedlight emitting regions). Plural n-type electrodes 112 formed between thelight emitting regions are electrically connected with each other on theover-all electrode section. After forming the n-type electrodes, it ispreferable to apply annealing at a temperature not higher than 700° C.

[0113] The over-all electrode section is used for the connection withoutside circuits.

Formation of the Insulation Film 113

[0114] Then the insulation film 113 is formed to fill the space betweenthe light emitting regions, so as to entirely cover the n-type contactlayer 103 that is exposed between the light emitting regions except forthe top surface of the p-type electrode 111 (FIG. 10, FIG. 15).

[0115] The insulation film 113 is formed so as to cover part of theinner periphery and outer periphery of the over-all electrode section ofthe n-type electrode 112. That is, the insulation film 113 is formed soas to expose the main part the over-all electrode section of the n-typeelectrode 112, and the exposed portions of the over-all electrodesection is used for the connection with outside circuits.

[0116] In the second embodiment, the insulation film 113 also serves asthe mirror film located at the end face of the light emitting regions200, and is therefore formed as a multi-layer film combining a lowrefractive index material layer and a high refractive index materiallayer, for example, a multi-layer film of dielectric materialscomprising two or more pairs of (SiO₂/TiO₂). This constitution allows itto increase the reflectivity by increasing the number of pairs oflayers. While SiO₂ is used as the low refractive index material and TiO₂is used as the high refractive index material to form the multi-layerfilm that constitutes the insulation film 113 in the example describedabove, the present invention is not limited to this constitution and thefollowing materials may also be used to form the multi-layer film thatserves as the mirror film. For the low refractive index material layer,MgO₂, Al₂O₃, SiON, MgO and the like can be used besides SiO₂. For thehigh refractive index material layer, ZrO₂, Nb₂O₅, Ta₂O₅, SiN_(x), AlN,GaN and the like can be used besides TiO₂. By combining these materials,the multi-layer film of dielectric materials that does not absorb thelight of the emission wavelength can be formed.

Formation of the P Pad Electrode

[0117] Then a p pad electrode 121 is formed as shown in FIG. 16 thatcomprises a portion 121 a of round shape (a circle having a radiussubstantially equal to the radial dimension of the fan shaped lightemitting region with the center at the light emitting point) forconnecting the exposed p-type electrode 111 and a pad portion 121 b thatis connected to the round portion 121 a via the neck portion 21 c. The ppad electrode is formed from Ni (1000 Å)/Ti (1000 Å)/Al (8000 Å), forexample.

Formation of the N Pad Electrode

[0118] Then the n pad electrode 122 is formed on the n-type electrode112 that has been exposed, for the purpose of bonding for electricalconnection to the n-type electrode 112. The n pad electrode is formedfrom Ni (1000 Å)/Ti (1000 Å)/Al (8000 Å), for example.

[0119] The concentrating point emission type light emitting element ofthe second embodiment that has the electrode arrangement shown in FIG.17 is manufactured as described above.

[0120] Since the concentrating point emission type light emittingelement of the second embodiment that has the constitution describedabove has the waveguide formed in each light emitting region, lightemitted from the light emitting regions 200 is directed through thewaveguide toward the light emitting point, reflected on the conicalsurface of the cavity 152 and is output through the light emitting point150 that is the opening formed in the p-type electrode.

[0121] With this constitution, since light emitted from the lightemitting regions 200 is concentrated at the light emitting point 150 andis output therefrom, light emission with high luminance is achieved.

[0122] Also in the concentrating point emission type light emittingelement of the second embodiment, since the reflector surface havingconical shape is constituted from the cavity 152 of conical shape, spotlight of near true circle can be obtained.

[0123] Also in the concentrating point emission light emitting elementof the second embodiment, the cavity 152 of extremely small conicalshape of the diameter of the circular mask 151 can be easily formed, andsatisfactory spot light of single mode can be obtained.

[0124] Since the concentrating point emission type light emittingelement of the second embodiment has the stacked semiconductor structureformed with the gallium nitride compound semiconductor element, spotlight of relatively short wavelengths such as yellow, blue and violetcolors as well as ultraviolet region can be obtained.

VARIATION OF EMBODIMENT 2

[0125] Although the reflector surface having conical shape isconstituted from the cavity 152 of conical shape in the secondembodiment, the present invention is not limited to this constitutionand a refracting surface having conical shape may be formed as describedbelow, so that concentrated light is output from the light emittingpoint.

[0126] Specifically, as shown in FIG. 18, in the stacked semiconductorstructure located right below the light emitting point, such a recess ofpyramidal shape is formed so as to reach at least the n-typesemiconductor layer that expands toward the light emerging point, andthe recess is filled with a transparent material 152 a that has arefractive index higher than that of the active layer.

[0127] With the constitution described above, light emitted in the lightemitting regions and directed toward the light emerging point isrefracted due to the difference in the refraction index between thesemiconductor layer (mainly the active layer) and the transparentmaterial 152 a that has a high refractive index in the conical surfaceof the recess, so as proceed upward in the transparent material 152 a.

[0128] Thus light is output through the light emitting point 150 upward.

[0129] Effects similar to those of the second embodiment can also beachieved with the constitution described above.

[0130] Although the light emitting regions are formed in straight linesarranged radially around the light emitting point at the center in thesecond embodiment, the present invention is not limited to thisconfiguration and curved light emitting regions 201 may be formed asshown in FIG. 19.

[0131] Effects similar to those of the second embodiment can also beachieved and the light emitting regions may be made longer with theconstitution described above.

[0132] Although the concentrating point emission light emitting elementof the second embodiment is made in such a constitution that has thelight emitting regions of double heterojunction structure wherein then-type contact layer 103, the n-type cladding layer 104, the activelayer 105, the p-type cladding layer 106 and the p-type contact layer107 that are formed from gallium nitride compound semiconductor elementare grown one on another successively, the present invention is notlimited to this constitution and it suffices to employ such a structureas at least the active layer is capable of confining light in thedirection of thickness sandwiched by layers of higher refractive index(smaller band gap) than the active layer.

[0133] n-type and p-type optical guide layers may also be formed betweenthe n-type cladding layer 104 and the active layer 105 and between theactive layer and the p-type cladding layer 106.

[0134] Also the light emitting regions are formed in fan shape in thesecond embodiment, but the present invention is not limited to thisconfiguration.

[0135] Moreover, while gallium nitride compound is used in the secondembodiment, the present invention is not limited to this configurationand other semiconductors such as GaAs or InGaP may be used.

[0136] Furthermore, although the pyramidal surface is formed in conicalshape in the second embodiment, the present invention is not limited tothis configuration. For example, such a pyramidal surface may beemployed that consists of faces inclined so that light propagating inthe waveguide of the light emitting regions is refracted or reflected soas to be directed upward (perpendicular to the surface).

[0137] Also the second embodiment has been described by taking aparticular stacked semiconductor structure as an example, but thepresent invention is not limited to this constitution.

[0138] Besides the stacked semiconductor structure described above, forexample, such a stacked semiconductor structure may be employed asdescribed below: the buffer layer 102 having thickness of 200 Å made ofAlGaN, an undoped n-type GaN layer, the n-type contact layer 103 made ofGaN having total thickness of 4 μm doped with 2.5×10¹⁸/cm³ of Si, acrack prevention layer made of In_(x), Ga_(1-x)N (0.1≦x≦0.15) havingthickness of 1000 to 1500 Å, a cladding layer made of GaN, an n-typeguide layer having thickness of 2000 Å made of Si-doped (InGaN/GaN) ofsuper lattice structure, six sets of (GaN barrier layer/InGaN activelayer/GaN cap layer) for light emitting layer and a last barrier layermade of GaN are formed on the substrate 101 having a mask formedthereon. Then a p-type cap layer made of Al_(x)Ga_(x-1)N (0≦x≦0.35)doped with Mg having thickness of 100 to 350 Å, a p-type guide layerhaving thickness of 2000 Å or less made of Mg-doped (InGaN/GaN) of superlattice structure, a p-type cladding layer having thickness of 6000 Å orless made of Mg-doped GaN, and a p-type contact layer having thicknessfrom 150 to 200 Å made of Mg-doped p-type GaN may be formed successivelyinto stacked semiconductor structure.

[0139] Although the cavity 152 that is closed at the apex is formedbelow the light emitting point 150 in the second embodiment, the presentinvention is not limited to this configuration and a pyramidal cavity152 b (having pyramidal surface 153 b) that opens at the top may be usedas shown in FIG. 20.

[0140] Such a constitution with the cavity that opens at the top makesit possible to emit light to the outside more efficiently than theclosed cavity 152 (FIG. 21A) since light entering the cavity emerges tothe outside without being confined within the cavity as shown in FIG.21B.

What is claimed is:
 1. A point emission type light emitting elementcomprising a stripe ridge having an n-type layer, an active layer and ap-type layer that are formed from semiconductors on a substrate, so asto emit light from one end face of the stripe ridge, wherein the striperidge has a protruding portion on the end face and the surface of thelight emitting element is covered with an shading film except for thetip of the protruding portion.
 2. The point emission type light emittingelement according to claim 1; wherein said n-type layer, said activelayer and said p-type layer are made of nitride semiconductor.
 3. Amethod for manufacturing a point emission type light emitting element byforming a plurality of elements on a substrate and dividing thesubstrate into individual elements comprising; a step of forming then-type layer, the active layer and the p-type layer on the substrate oneon another, a step of forming stripe ridge so as to form neck portionsin correspondence to one end of said each element, said neck portionhaving narrower width than the other portion, a step of forming shadingfilms at least on one end face of the stripe ridge and the top surfaceand both side faces of the neck portion, and a step of dividing theelements at the neck portion along a direction perpendicular to thelongitudinal direction of the stripe ridge.
 4. A concentrating pointemission light emitting element comprising a stacked semiconductorstructure in which an active layer is sandwiched by a p-typesemiconductor layer and an n-type semiconductor layer that have band gaplarger than that of the active layer to compose double heterojunctionstructure, wherein a light emitting point for emitting a light islocated in the surface of the p-type semiconductor layer to compose asurface emission type light emitting element, wherein a pyramidalsurface which is located right below the light emitting point and whichreflects the light upward or refracts the light is provided in thestacked semiconductor structure, wherein the stacked semiconductorstructure is divided into a plurality of light emitting regions locatedaround the pyramidal surface that is at the center, and ridges ofsmaller width than the light emitting region are formed on the p-typesemiconductor layer of said light emitting regions respectively so thatlight emitted at the light emitting regions is directed toward thepyramidal surface.
 5. The concentrating point emission light emittingelement according to claim 4, wherein a plurality of light emittingregions is formed by separating the light emitting regions from eachother by etching the borders between adjacent light emitting regions toa depth midway in the n-type semiconductor layer in the stackedsemiconductor structure except for the light emitting point and avicinity thereof, and n-type electrodes are formed on surfaces of then-type semiconductor layer that has been exposed by etching.
 6. Theconcentrating point emission light emitting element according to claim4, wherein the pyramidal surface is constituted from a pyramidal cavitythat has an apex located in the light emerging direction and is formedin the stacked semiconductor structure.
 7. The concentrating pointemission light emitting element according to claim 4, wherein thepyramidal surface can also is formed by filling a recess of pyramidalshape, that expands toward the light emerging point and is formed so asto reach at least the n-type semiconductor layer in the stackedsemiconductor structure, with a transparent material having a refractiveindex higher than that of the active layer.
 8. The concentrating pointemission light emitting element according to claim 4, wherein thepyramidal surface is a conical surface.
 9. The concentrating pointemission light emitting element according to claim 5, wherein thepyramidal surface is constituted from a pyramidal cavity that has anapex located in the light emerging direction and is formed in thestacked semiconductor structure.
 10. The concentrating point emissionlight emitting element according to claim 5, wherein the pyramidalsurface can also is formed by filling a recess of pyramidal shape, thatexpands toward the light emerging point and is formed so as to reach atleast the n-type semiconductor layer in the stacked semiconductorstructure, with a transparent material having a refractive index higherthan that of the active layer.
 11. The concentrating point emissionlight emitting element according to claim 5, wherein the pyramidalsurface is a conical surface.